892 CHARLES PauL ALEXANDER 
G. canadensis is most commonly found along small streams near cliffs; 
G. dwersa, resting on vegetation along running water or clinging to vertical 
wet banks; G. rostrata, on rich vegetation in damp places, where it is often 
extremely abundant (Alexander, 1912:67-68). The habits of the adult 
flies are discussed on page 878. 
Genus Discobola Osten Sacken 
1865 Discobola O.8. Proc. Ent. Soc. Phil., p. 226. 
1869 Trochobola O. 8. Mon. Dipt. N. Amer., part 4, p. 98. 
The genus Discobola is a well-defined group including eight described 
species with a curious discontinuous distribution — two species occurring 
in North America, two in Europe, and four in New Zealand. The species 
are readily distinguished by the presence of a strong supernumerary 
cross-vein between the two anal veins. The only local species is D. 
argus. 
Discobola argus (Say) 
1824 Limnobia argus Say. Long’s Exped., App., p. 358. 
1865 Discobola argus O. 8. Proc. Ent. Soc. Phil., p. 226. 
The species Discobola argus is a curious fly, with ocellate markings on 
the yellowish white wings (Plate XXXII, 41). The body coloration is 
yellowish, the thorax with three brown stripes, each femur with a brown 
subterminal ring. The immature stages of the American species are 
unknown but are probably spent in decaying pine stumps, as are those 
of the European D. caesarea; specimens of D. argus have been observed 
mating on the bark of stumps (in Ithaca, New York, October 3, 1912, 
by Ilg and Alexander). The fly is uncommon in May and June but 
becomes more numerous from August to October. 
Genus Rhipidia Meigen 
1818 Rhipidia Meig. Syst. Beschr., vol. 1, p. 153. 
In the genus Rhipidia there are about twenty-eight described species, 
most numerous in the tropics of the New World. The character of the 
pectination of the antennae (page 851) varies in the different groups or 
subgenera as follows: 
Rhipidia Meig. (maculata, bryanti) — antennae of the male bipectinate. - 
Monorhipidia Alex. (fidelis) — antennae of the male unipectinate. 
Arhipidia Alex. (domestica, shannoni) — antennae of both sexes subpectinate to simple. 
